Fluid power conversion apparatus such as a turbine-generator combination or an electrically-driven continuous flow pump, an example of which is shown in FIG. 1, typically has an external motor 105 driving the pump 106 which causes fluid flow through pump 106 in direction A. Since the process is reversible, the same configuration can be used to convert fluid flow to electrical power. In such a case, a turbine 106 is driven by the kinetic energy of fluid flow through turbine 106 in direction B and drives an electrical generator 105 that is placed outside the turbine housing.
In both of these cases, the drawback of separating the functions of the motor and the pump (or the turbine and the generator) is that it requires that a shaft 102 pass through a housing penetration 100. Housing penetration 100 requires a rotary seal 101 between shaft 102 and housing 103 to prevent escape of the fluid or the ingress of ambient air. In both cases, an external bearing 104 is needed to support shaft 102 connected to impeller 107.
Another drawback of such systems is that a bend in the inlet or outlet duct 103 is needed to allow shaft 102 to exit in line with impeller 107, disturbing the natural flow direction of the fluid and adversely affecting efficiency. Also, the presence of shaft 102 in the flow creates turbulence and drag, also adversely affecting efficiency.
A further drawback is that the bend in duct 103 complicates the installation, especially in locations with tight space requirements. Installation with in-line flange connections is not possible.
Lastly, the motor or generator is a separate entity from the pump or turbine, requiring that these components be installed so as to maintain the alignment of the shafts of each of the pair of components. This requires that a coupling 108 be placed in between the pair of shafts. The motor and pump or turbine and generator need to be mounted to a common base (not shown) to maintain such alignment during operation and to transmit the generated torque from one to the other.
To adapt the high rotational speed of an electric motor/generator to the lower speed of the pump/turbine, a gearbox is frequently placed between pump/turbine and motor/generator, adding another component which then requires yet another coupling. Alignment between motor/generator and pump/turbine are required, and the torque compensation provided by a common base is also necessary.
An electric motor or generator rejects heat during the consumption or generation of electric power and requires the removal of the heat through an external cooling system for the motor or generator.
These drawbacks, which result in higher costs, inefficient operation and inefficient use of space, are summarized in the following list:                the need for a drive shaft, fluid seal and external bearing;        separate components resulting in high acquisition costs;        flow turbulence caused by the duct bend and the drive shaft;        the duct bend complicating installation and preventing in-line installation;        the need to align and install separate components on a common base;        the need for a gearbox further complicating the installation; and        the need for an external cooling system.        
The present invention arranges the fluid power conversion apparatus by combining the impeller and the motor/generator rotor concentrically and in radially-coincidental planes whereby the armature windings are outside the fluid flow path at the pump periphery, and the armature is fixed to an outer housing. The motor/generator rotor is attached directly to the impeller at the periphery of the impeller blade tips.
The present invention eliminates all extraneous requirements of the conventional pump or turbine as described above, namely the drive shaft, the external bearing, the shaft seal, the bend in the duct, the installation and alignment of the motor/generator, a common installation base, a gearbox, and the external cooling requirements of the motor/generator. All of this is accomplished by integrating the motor/generator with the pump/turbine impeller in a more efficient and compact way.
The motor/generator rotor is affixed directly to the pump/turbine impeller and is “wet” (exposed to the fluid flow) while the armature with windings is located outside the fluid flow pump/turbine housing. The gap between armature and rotor is situated at a greater diameter from the centerline than is economically practical with a suitable conventional electric motor or generator so that more torque can be generated and more power can be transmitted at lower shaft speed than in an otherwise identical motor envelope. The fluid is forced through the rotor/armature gap to cool the motor/generator by the pressure difference between the intake and outlet side of the impeller. An impeller support bearing serves as a common bearing for both pump/turbine and motor/generator.
The wet rotor consists of magnets and encapsulating material and contains no electrical windings or brushes, thereby eliminating the need to keep the rotor dry. The larger diameter of the rotor of the electric motor/generator in combination with electronic speed control/power conditioning can perform the function of a conventional gearbox.
In a hollow rotor design that is entirely supported at the periphery, the bearing and the water seal are placed at the periphery of the rotor around the impeller. This requires an expensive, large diameter bearing and seal and is difficult to maintain over extended periods of operation. In the present invention, the impeller/rotor bearing is not placed at the periphery of the impeller but at the centerline of the pump/turbine, and the support is supplied by a hub held in place by the pump/turbine diffuser stator vanes.
U.S. Pat. No. 5,490,768 (Veronesi et al.) discloses an electrically-driven waterjet propulsion system in which the electric motor portion is placed forward of the pump over the reduced-diameter suction portion of the rotor. The rotating portion is supported by a peripheral bearing 54 as well as bearings 56 and 58 mounted inside the impeller hub 30. The combined arrangement, as a result of the motor portion being placed in front of the pump, considerably lengthens the waterjet intake. Moreover, it places the intake opening on the bottom of the vessel hull substantially farther forward, unfavorably affecting waterjet performance (increasing the likelihood of picking up boundary air at high speeds). Furthermore, placing the motor forward of the pump greatly increases the requirement for structural support and the complexity of additional structure, both resulting in increased weight and cost.
In addition, Veronesi et al. utilize water-lubricated bearings for each of the three bearings 54, 56 and 58. Water-lubricated bearings are by nature less precise than precision roller bearings, thus requiring both a larger gap tolerance and an impeller peripheral clearance, resulting in loss of overall system efficiency. Further, the AC-powered squirrel cage motor in such systems has severe limitations in power density (power output per volume of the apparatus), thus causing a scale mismatch between the capability of the electric motor and the waterjet positioned therein and powered thereby. The motor can only provide a fraction of the power that the waterjet would be capable of providing.